1. Field of the Invention
This invention relates to a process for producing an elastomeric polymer derived mainly from a conjugated diene. More specifically, it relates to a process for producing a conjugated diene polymer which comprises polymerizing a conjugated diene, or copolymerizing a conjugated diene with another conjugated diene or a monovinyl aromatic compound, at a temperature in the range of about 30 to about 100.degree. C. in the presence of a catalyst composed of an alkenyl sodium and a sodium alkoxide of a dimethylalkyl carbinol.
2. Description of the Prior Art
Polymerization of a conjugated diene, or copolymerization of a conjugated diene with another conjugated diene or a monovinyl aromatic compound, which is catalyzed with an alkali metal or alkali metal compound as a catalyst, is widely known.
Alfin catalysts and a metallic sodium catalyst have heretofore been used as catalysts containing an organic sodium compound or metallic sodium in the polymerization of conjugated dienes with or without monovinyl aromatic compounds.
It is well known that the alfin-catalyzed polymerization of conjugated dienes with or without monovinyl aromatic compounds results in a rapid rate of polymerization, provides polymers having a wide molecular weight distribution in high yields, and results in a trans-block of butadiene, and that rubbers obtained by vulcanizing the resulting polymers have superior properties such as high abrasion resistance, tensile strength and flex resistance. The production of alfin rubbers using alfin catalysts is described extensively in the literature including Morton, Rubber Age, Vol. 94, pages 87 to 92, October 1963.
Polymers obtained by polymerizing conjugated dienes with or without monovinyl aromatic compounds using alfin catalysts are too hard for use as a rubber and have many undesirable properties because they have extremely high molecular weights with a wide distribution of molecular weight and result in a trans-block of butadiene, i.e., a block of butadiene units bonded with trans linkages.
A polymerization catalyzed with metallic sodium, on the other hand, has the disadvantage that the proportion of 1,2-bonds of butadiene is increased and a high polymer is very difficult to produce.
A polymerization of conjugated dienes with or without monovinyl aromatic compounds which is catalyzed with an organolithium industrially results in the production of random copolymers and block copolymers.
It is known as described in Japanese Patent Application (OPI) No. 68686/73, for example, that organopotassium compounds can be used to catalyze the polymerization of conjugated dienes, but not on an industrial scale.
The present invention pertains to a catalyst composition comprising an alkenyl sodium and a sodium alkoxide of a dimethylalkyl carbinol which on superficial examination might be considered similar in composition to alfin catalysts, but in fact is not similar and results in the production of polymers which are quite different from those produced using conventional alfin catalysts.
Morton in J. Am. Chem. Soc., Vol. 69, p.959 (1947), discloses that a catalyst composition composed of an alkenyl sodium and sodium tert.-butoxide does not exhibit the characteristics of an alfin catalyst in polymerization at room temperature, and as a result, concluded such was outside the definition of alfin catalysts.
Furthermore, Morton in Advances in Catalysis, Vol. 9, p.746 (1957), disclosed that when sodium tert.-butoxide was used instead of sodium isopropoxide in a typical alfin catalyst, the yield of polymer drastically decreased from 75% to only 7%, and there was a marked decrease in molecular weight, thus demonstrating the characteristics of such a catalyst composition as an alfin catalyst did not exist.
Relatively recently, R. Lenz disclosed in Organic Chemistry of Synthetic High Polymers, p. 637, (1967), that alcohols other than secondary alcohols do not give rise to any appreciable alfin catalyst activity.
Thus, from these disclosures in the prior art combinations of an alkenyl sodium and sodium tert.-butoxide have heretofore been excluded by those skilled in the art from inclusion within the definition of alfin catalysts.